Accurate image-on-paper registration is an important aspect in the printing and image reproduction industry. Single-sided (or “simplex”) registration is concerned with adjusting the position of a printed image with respect to the edges of the printing medium. Double-sided (or “duplex”) image-on-paper registration poses additional challenges, since it needs to make sure that the image position on the back side accurately matches the image position on the front side of the printing medium, so to avoid “show-through” effects. Shrinkage of the paper that may occur during the printing is an additional concern for the duplex registration. Due to the shrinkage, the paper may be smaller when the duplex image is transferred than it was for the simplex image. Depending on the printing medium and ink, there may be significant variations in the shrinkage factor.
Registration marks have conventionally been used to assist both in the simplex and in the duplex registration. These marks are printed on the front side and/or back side of the printing medium, and a horizontal distance and vertical distance between the marks and the respective edges of the printing medium are measured. These measurements allow to adjust the position of the image on the paper for subsequent printouts. Triangular marks for manual measurements have conventionally been used. But manual measurements are slow and cumbersome, and the triangular marks are not particularly well-suited for automatic image-on-paper registration. Some printers feature an automatic image-on-paper registration. These printers print a fiducial mark pattern on the front side and/or back side of the printing medium. A scanner is then employed to scan the printed medium and the fiducial marks, and the distance between the edges of the printing medium and the fiducial marks is determined automatically from the scanned representation of the printing medium. But these known systems have sometimes failed to provide sufficiently accurate distance measurements, resulting in an insufficient adjustment of front-to-back printing. Some known systems require an undesirably long time to perform an image-on-paper registration.
The present invention overcomes these and other shortcomings of the prior art and provides an improved method and system for determining and adjusting a printing position.